<html>
  <head>
    <style>
      div {
        background: green;
        width: 100px;
        height: 100px;
      }
      span {
        background: yellow;
        width: 50px;
      }
    </style>
  </head>
  <body>
    <div>
      <span></span>
    </div>
  </body>
</html>
